Panel loudspeakers essentially consist of a panel-shaped membrane (sound panel), a drive system (driver) and a support. The panel-shaped membrane should be light-weight and, more particularly, should resist bending. The drive system of panel loudspeakers typically includes one or more electromechanical (piezo-electric or preferably electrodynamic) converters. The support transmits the weight of the panel-shaped membrane and of the drive system to a rigid support member without inhibiting the intended movement of the membrane.
Conventionally designed panel loudspeakers (planar devices) operate below resonance, i.e., the panel constructed to operate in a frequency range below the first bending oscillation resonance. This operating mode is known from conventional cone loudspeakers and is frequently referred to as piston loudspeaker. Accordingly, as with the piston loudspeaker, bending oscillations of a planar device (rigid panel loudspeaker) are prevented (which necessitates a complex design).
Modern panel loudspeakers, on the other hand, operate at resonance, i.e., constructive measures are employed to ensure that the panel attains bending oscillation resonances when operating in the intended operating frequency range. This loudspeaker operating mode is also referred to as multi-resonance panel loudspeaker. Sometimes, the term “bending wave loudspeaker” is used which has multiple definitions as it could refer to both a multi-resonance panel loudspeaker and non-resonant absorber panels operating with bending waves. The conventional multi-resonance loudspeakers are almost exclusively panel-shaped, direct-radiating loudspeakers that can be used without a housing and can be installed, for example, as ceiling loudspeakers in suspended building ceilings or operated freestanding, like a sign stand with a base.
If a multi-resonance panel loudspeaker without a housing is placed close to a sound-reflecting wall (distance from the wall less than the panel diagonal, orientation parallel), then a decrease in the power is generally observed at low frequencies (wall effect). The “wall effect” can be lessened by shielding the multi-resonance panel loudspeaker with a rear-mounted flat housing. However, although this solution is adequate for small panels that are easy to handle, the bandwidth still suffers.
Large flat panel loudspeakers have theoretically the following advantages: a reduced lower cutoff frequency is attained through self-diffraction, with the additional advantage that the lowest panel resonance is are relatively low. In addition, large flat panel loudspeakers have a high sensitivity due to the large area of their membrane, since the radiated power is proportional to the membrane area and proportional to the square of the average effective acoustic velocity on the membrane. In addition, the small excursion of the drivers causes only relatively small nonlinear distortions. Also, with the large panel surface area, the square of the acoustic velocity can be made smaller while still being able to radiate the same acoustic power. Finally, the large area can also radiate a relatively high peak power.
Conversely, other large flat panel loudspeakers (planar devices, electrostatic devices and magnetostatic devices) all have the serious focusing problem: in the high frequency range, the solid angle narrows with the square of the ratio of wavelength to membrane diagonal. For example, with a distance of five meters between the listener and the loudspeaker, the ear of the listener would have to be positioned exactly on the mid-perpendicular of the panels with an accuracy of five centimeters. This can rarely be achieved in practice. Large electrostatic devices (flat panel loudspeakers with a soft membrane) require additional complex high power electronics operating at high-voltages. Large magnetostatic devices (also flat panel loudspeakers with a soft membrane) require large, expensive, heavy-weight flat magnet drivers which pose an additional disadvantage. Large planar devices (flat panel loudspeakers with a rigid membrane) are severely limited in their operating frequency band: the first bending wave resonance frequency which represents a significant cutoff frequency, decreases with the square of the panel diagonal.
Of the four operating modes of large flat panel loudspeakers being considered (planar, electrostatic, magnetostatic, multi-resonance panel loudspeaker), only the multi-resonance panel loudspeakers have all the aforedescribed advantages of large flat panel loudspeakers (cutoff frequency, sensitivity, distortion, power reserve) without the aforedescribed disadvantages (focusing effect, need for expensive high-voltage flat magnet drivers, limited operating frequency band). However, like with other large flat panel loudspeakers, selecting a suitable support structure also presents a problem with the multi-resonance panel loudspeakers. Large freestanding walls of any kind require expensive support and safety structures. As a result, only small to medium-size multi-resonance flat panel loudspeakers have been realized to date, with many of the aforedescribed advantages either absent or implemented only on a limited base.
It is therefore an object of the invention to provide a flat panel loudspeaker arrangement which eliminates the disadvantages described above.